Internal combustion engines having intake and exhaust valves are well known. A typical internal combustion engine includes at least one camshaft having lobes for opening and closing the valves. In some engines, separate camshafts are provided for the intake and exhaust valves; thus each of the twin camshafts has only half of the total number of cam lobes.
In modern internal combustion engines, each valve train typically includes a hydraulic valve lifter (HVL) for automatically eliminating mechanical lash in the valve actuating mechanism. A spring urges a piston outwards to eliminate lash, and in response the piston chamber fills with oil via a check valve. Although oil can slowly enter and leave the piston chamber, during any relatively short period of engine operation, for example, one or a few revolutions, the HVL is hydraulically rigid.
A condition can arise when an engine is shut down, in that some valves are left in the open position with the full pressure of the valve closing spring brought to bear against the corresponding HVL. Over time, when the engine is not running, the oil in the HVL chamber is forced out as the piston assumes a compliant position. When the engine is restarted, the piston chamber will be refilled as engine control is re-established and the engine oil supply pressure increases, but for the first few seconds of operation, the deflated HVL can be objectionably noisy (known in the art as “cold start noise”) and can also cause excessive engine wear. This problem is aggravated by the trend in the HVL art to smaller piston chambers, having lower reservoir volumes, to reduce the overall size of the lifters. In addition, special HVLs for use in valve deactivation on some engines have especially small piston chambers and are therefore especially vulnerable to leakdown under stopped, valve-open load.
In prior art engines, the position of the engine when it stops is essentially random; that is, there is no mechanically or electronically favored angular position of the crankshaft or camshafts after the engine is shut off and coasts to a rotational stop. The number of valves open and degree of valve opening at engine stop depend upon engine configuration, i.e., L4, V6, V8, etc., as well as the number of camshafts and the cylinder firing order. However, some angular positions are favored over others. For example, for the purpose of reducing cold start noise, it is desirable to bring the engine to a stop position where none of the engine valves are at full open position. Hence, if an optimal angular position can be determined, then it is desirable to be able to bring the engine to a stop at that position at every shutdown.
It is a principal object of the present invention to minimize the number of valves left open and the degree of valve opening at every shutdown of an internal combustion engine, and thereby minimize cold start noise upon restarting of the engine.